Loudspeakers are generally known in the art. A loudspeaker generally comprises a permanent magnet and a voice coil through which an electrical signal is passed. The interaction between the current passing through the voice coil and the magnetic field produced by the permanent magnet causes the voice coil to oscillate in accordance with the electrical signal. It is desirable to have the voice coil move through a small circular gap, the magnetic field being concentrated across the gap. In U.S. Pat. No. 3,358,089 there is shown a loudspeaker where the magnet is cup-shaped and has a cylindrical pole-piece located in the center of the cup, and a disk located on the upper edge of the cup. The shape of the magnet, the pole-piece and the disk serve to direct the magnetic field across a gap between the pole-piece and the disk. U.S. Pat. Nos. 3,296,386; 3,453,400; 3,953,687; and 3,881,074 show loudspeakers where the permanent magnet is a flat, annular element. These loudspeakers have a pole-piece which is generally cylindrical and extends through the central hole of the annular magnet, and a back plate upon which the magnet rests. An annular end plate is placed on the side of the magnet opposite the back plate. The magnetic field is concentrated into the gap between the pole-piece and the annular end plate. In the speaker shown by U.S. Pat. No. 3,953,687, the cylindrical pole-piece is separate from the disk-like back plate and the back plate is tapered to save material. In U.S. Pat. No. 3,453,400 there is shown a loudspeaker with a pole-piece integrally formed with a radially tapered back plate. The thickness of the back plate is taught to be equal to the thickness of the pole-piece.